I was very nervous before my first deep dive. It actually took a few deep dives before I was comfortable with them, and now I even look forward to them. Mental preparation for deep dives is something you might need to work on – it’s easy for one’s imagination to run wild when it’s an unfamiliar skill.
If you haven’t done a deep dive before, there are some things that you might want to know in advance:
- There will be a boat ride. You’ll roll over the side of the boat on the skipper’s count, along with the other divers. Don’t roll over late – rather stay on the boat and let the skipper drop you again when everyone has moved clear. If you land on another diver it’s a good way to ensure you won’t get invited for any more boat dives!
- You will probably descend on a shot line. This is a weighted line with a buoy on the end, and the skipper will drop it close to the reef or wreck you plan to explore. You’ll use the line to make sure that you find your dive site – you’ll be descending through a large water column, and a current can easily carry you away from your destination. Circle the shot line gently with two fingers and use it as a guide while you descend. DO NOT grip it like a monkey!
- If you’re diving in Cape Town, it’ll be cold. And it’ll get colder the deeper you go. It might even be dark, too. The first 10-15 metres of water may be very murky and green, but down below that the visibility will probably improve, even if it’s dark.
- You will feel stupid. At about 25 metres, nitrogen narcosis becomes a noticeable issue. If you feel weird, ascend a bit, wait for it to dissipate, and then resume your descent – SLOWLY. But even if you don’t get it severely, your mental abilities WILL be limited. This is a fact of deep diving on air. You might find your field of vision narrows a bit, that you obsess over things, or that you are very conscious of only being able to do one thing at a time. All this means you need to take extra care, and don’t be reckless. Stay close to your buddy and watch each other carefully.
- You will feel heavy at the bottom – no matter how much or how little weight you are wearing. Don’t wait until you’re at 30 metres to start inflating your BCD. Stop at 10 metres, slow your ascent, and inflate your BCD slowly as you continue going down. This way you won’t rocket into the sand at the bottom (assuming there IS a bottom within the range of scuba – not the case if you’re diving a wall) like a cannonball, the chances of severe nitrogen narcosis are minimised, and you can be in control of your buoyancy all the way down.
- Colours will be dim and greyish. Take a torch – you may not think it’ll make a difference, but even at 20 metres the reds and oranges are significantly diminished and by 30 metres you just won’t see them at all without artificial light. One of the joys of deep diving is illuminating a very ordinary object and seeing the colours pop out at you.
- Swimming will be more of an effort than usual. The water will feel a bit like molasses – thick and viscous. You’re under tremendous pressure, and you simply won’t be able to dart around like a mosquito. Take it slow, don’t over-exert, and move at the speed of natural creatures.
- The dive will be short. This is for two reasons: first, you will use your air up very quickly at depth. If it is your first deep dive, this will be especially true – you’ll be nervous, or excited, and you won’t have the experience that enables you to reduce your air consumption. Second, your no-decompression time decreases the deeper you go. So even if you have lots of air, you will only be able to spend 20 minutes or so at the bottom before you have to ascend. If you can’t remember what no-decompression time is, it’s time to revise your dive tables!
- You will do a safety stop. Don’t be slack with this – it is absolutely vital. You’ll ascend slowly, maybe stop at 10 or 15 metres for a little bit, and then do a safety stop of at LEAST 3 minutes at 5 metres. Your cylinder will be quite empty, so you’ll be buoyant. Make sure that you control your buoyancy very carefully. Watch the Divemaster, your computer, or the reel on the DM’s buoy line (he may let it hang in the water next to him) to ensure that you stay at a constant depth. Your depth gauge will respond slowly to changes in depth, so it’s not hugely reliable at this stage of the dive.
- You might deploy a surface marker buoy (SMB). Your instructor may get you to do this yourself, for practice. An SMB (or as I like to call it, a safety sausage!) is a long tube on a line, usually orange or yellow, that you inflate with air from your octo (NOT your regulator). One end is closed (the top) and one end is open for you to put your octo into and press the purge button to fill it with air. It stands up straight in the water, and warns passing boats that there are divers about to surface. It also shows the skipper of your boat where you are, so that he can be nearby to fetch you. When inflating the SMB, hold onto the line attached to it – not the tube itself, or you might be pulled out of the water with it when you inflate it. Don’t fill it to capacity if you’re still at the safety stop – just a couple of purges of your octo will be enough. As it ascends the air will expand and when it reaches the surface the SMB will be sufficiently inflated to stand vertically out of the water.
Gerard demonstrates correct safety stop technique in Sodwana In the photo above, note how Gerard is watching his dive computer for depth and while it counts down his safety stop, hanging onto his SMB while he waits to ascend.
- There should be a hang tank for you to breathe off at the safety stop. A hang tank is a spare cylinder of air, with several regulators attached. It allows you to complete your safety stop without worrying about being low on air, if that’s the case. It also provides a useful reference for keeping yourself at a constant depth while you’re degassing!
Divers breathing from a hang tank in Smitswinkel Bay
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